The invention relates to a method for starting up a switched-mode power supply, as well as a switched-mode power supply having a starting circuit, in which the alternating voltage inputs of a bridge rectifier, at which an alternating voltage is adjacent, are connected with one another through a Y capacitor or a series circuit of two Y capacitors, in which a parallel circuit, made up of a first capacitor and a series circuit made up of the primary winding or coil of a first transformer and a first controllable switch, is connected to the direct voltage outputs of the bridge rectifier, whose control input is connected with the output of a pulse generator, and in which a series circuit of a first diode and a second capacitor is situated parallel to the secondary winding of the transformer.
The prior art includes providing a battery or an accumulator for starting up a switched-mode power supply.
However, the prior art method for starting up a switched-mode power supply has the disadvantage that the manufacturing costs are relatively high, and the endurance or life of the battery or of the accumulator is limited.
It is accordingly an object of the invention to provide a method for starting up a switched-mode power supply, and switched-mode power supply having a starting circuit that overcome the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that requires only a low technical outlay, has low manufacturing costs, and guarantees the endurance over a long period of time.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method for starting up a switched-mode power supply, including the steps of providing a bridge rectifier having alternating voltage inputs, a control input, and direct voltage outputs, disposing an alternating voltage at the alternating voltage inputs of the bridge rectifier, connecting the alternating voltage inputs with one another through a Y capacitor circuit including one of a Y capacitor and a series circuit of two Y capacitors, providing a first transformer having a primary winding and a secondary winding, providing a first series circuit made up of the primary winding of the first transformer and a first controllable switch, connecting the control input of the bridge rectifier with an output of a pulse generator, connecting a parallel circuit made up of the first series circuit and a first capacitor to the direct voltage outputs of the bridge rectifier, connecting a second series circuit made of a first diode and a second capacitor in parallel to the secondary winding of the first transformer, transmitting energy collected by the Y capacitor circuit to the second capacitor, and driving the controllable switch by producing pulses with the pulse generator dependent on a voltage tapped at the second capacitor.
In accordance with another mode of the invention, the energy collected by the Y capacitors is transmitted to the second capacitor, and the pulse generator produces drive, trigger, or control pulses for the controllable switch dependent on a voltage that can be tapped at the second capacitor.
In accordance with a further mode of the invention, preferably, the pulse generator begins to produce drive pulses for the controllable switch only when the voltage at the second capacitor has exceeded a first threshold value. According to a specific embodiment of the invention, it is thereby provided that the voltage that can be tapped at the second capacitor is applied as a supply voltage to a supply voltage input of the pulse generator only when it has reached a first predeterminable minimum value in order to switch on the pulse generator.
In accordance with an added mode of the invention, preferably, the pulse generator produces no drive pulses when the voltage at the second capacitor has decreased below a second threshold value, whereby the second threshold value is smaller than the first threshold value. If the pulse generator is switched on, it receives current from the second capacitor, resulting in a lowering of the voltage that is adjacent over the second capacitor. Because the first threshold value, upon the reaching of which drive pulses are produced, is higher than the second threshold value, with no drive pulses being produced when the value falls below this second threshold value, the invention prevents the situation where the production of the drive pulses is immediately terminated again when there is a slight decrease of the voltage at the second capacitor at the beginning of the production of the drive pulses.
In accordance with an additional mode of the invention, the pulse generator has a supply voltage input, and the voltage tapped at the second capacitor is applied to the supply voltage input of the pulse generator only when the voltage tapped at the second capacitor reaches a first predeterminable minimum value.
In accordance with yet another mode of the invention, a control unit is connected to the pulse generator for controlling the pulse generator and the voltage tapped at the second capacitor is applied to the control unit only after a predeterminable time period after a switching on of the pulse generator.
In accordance with yet a further mode of the invention, there is provided a third series circuit made up of a second diode and a third capacitor, a second secondary winding of the first transformer is connected in parallel to the third series circuit, a voltage with the second secondary winding of the first transformer is produced at the third capacitor and the voltage tapped at the second capacitor is applied to the control unit when the voltage at the third capacitor reaches a second predeterminable minimum value.
With the objects of the invention in view, there is also provided a switched-mode power supply having a starting circuit, the power supply including a bridge rectifier having alternating voltage inputs to be connected to an alternating voltage, at least one direct voltage output, and a control input, a plurality of Y capacitors including two Y capacitors connected in series to form a first series circuit having a first common connection point, the alternating voltage inputs of the bridge rectifier connected with one another through one of the group consisting of one of the Y capacitors and the first series circuit, a pulse generator having an input and an output, a transformer having a primary winding and a secondary winding, a controllable switch connected in series to the primary winding to form a second series circuit, a first capacitor connected in parallel to the second series circuit to form a parallel circuit, the parallel circuit connected to the at least one direct voltage output of the bridge rectifier, the control input of the bridge rectifier connected to the output of the pulse generator, a first diode and a second capacitor connected in series to form a third series circuit having a second common connection point, the third series circuit connected in parallel to the secondary winding of the transformer, a second diode connecting the first common connection point to the second common connection point, and a signal supply device supplying a signal dependent on a voltage over the second capacitor to the input of the pulse generator.
In accordance with yet an added feature of the invention, the common connection point of the two Y capacitors is connected with the common connection point of the first diode and the second capacitor through a second diode, and a signal dependent on the voltage over the second capacitor is supplied to an input of the pulse generator, dependent on which the pulse generator produces drive pulses for the controllable switch.
In accordance with yet an additional feature of the invention, a system having a first threshold value detector and a second controllable switch is connected between the second capacitor and the pulse generator. The first threshold value detector is situated parallel to the tapping of the voltage at the second capacitor, whereby the output of the threshold value detector is connected with a control input of the second controllable switch, which connects a supply voltage input of the pulse generator with the common connection point of the first diode and the second capacitor. The threshold value detector preferably has a hysteresis characteristic; i.e., the second controllable switch is driven conductive when the voltage over the second capacitor reaches a first threshold value, and the second switch is blocked or disabled when the voltage over the second capacitor decreases below a second threshold value, the second threshold value being smaller than the first threshold value. In this specific embodiment, the pulse generator is switched on for the production of drive pulses when the second switch is switched on, and the voltage that is adjacent over the second capacitor is applied to the pulse generator as a supply voltage, and the pulse generator is switched off when the second switch switches off.
To charge the second capacitor, which acts as a smoothing capacitor in the secondary circuit, according to the inventive method or in the inventive switched-mode power supply at least one capacitor is connected to the alternating voltage inputs of the bridge rectifier of the switched-mode power supply, and the energy collected by this capacitor is transmitted, through a diode, to the smoothing capacitor connected to the secondary winding of the transformer. It is particularly advantageous to use the Y capacitors, which in many switched-mode power supplies are for safety reasons already connected to the alternating voltage inputs, to collect the energy.
As soon as the smoothing capacitor has been charged to a predeterminable minimum voltage, this minimum voltage is applied to the supply voltage inputs of the pulse generator of the switched-mode power supply to switch it on. Because the pulse generator now emits switching pulses to the controllable switch in the primary circuit of the switched-mode power supply, in the secondary circuit the output voltage of the switched-mode power supply is slowly built up.
A construction of the inventive method provides in the transformer a second secondary winding to which a series circuit of a diode and an additional capacitor is connected, which is now charged because the pulse generator clocks or supplies the switched-mode power supply with clock pulses, or operates the switched-mode power supply in switching mode. As soon as the voltage at this additional capacitor reaches a predetermined minimum value, the output voltage of the switched-mode power supply, which can be tapped at the smoothing capacitor, is applied to the supply voltage of a control unit that controls the pulse generator, preferably, a microprocessor, to switch it on. The switched-mode power supply is now ready for operation, and can supply a load with a regulated voltage.
In accordance with again another feature of the invention, the input of the pulse generator has a supply voltage input and a control input, the transformer has a second secondary winding, a third diode and a third capacitor are connected in series to form a fourth series circuit, the second secondary winding is connected in parallel with the fourth series circuit, a second threshold value detector has an output, a control unit has a supply voltage input and a control output connected to the control input of the pulse generator, a second controllable switch has a control input, the second controllable switch connecting the supply voltage input of the pulse generator to the supply voltage input of the control unit, the second threshold value detector is connected in parallel to the third capacitor, and the output of the second threshold value detector is connected to the control input of the second controllable switch.
In accordance with again a further feature of the invention, there is provided a fourth diode and a fourth capacitor connected in parallel to the fourth diode to form a second parallel circuit, the second parallel circuit disposed between the two Y capacitors.
In accordance with again an added feature of the invention, there is provided at least one fifth diode disposed between the second controllable switch and the supply voltage input of the pulse generator.
In accordance with again an additional feature of the invention, there is provided a second transformer having a primary winding and a secondary winding, an RC element having a fifth capacitor and a first resistor, the output of the pulse generator being a control output connected through the RC element to the primary winding of the second transformer, and the secondary winding of the second transformer being connected with the controllable switch.
In accordance with still another feature of the invention, the bridge rectifier has a direct voltage terminal connection, the controllable switch has a terminal connection, the secondary winding of the second transformer has a terminal connection, a fourth diode and a fourth capacitor are connected in parallel to form a second parallel circuit having a third common connection point, the second parallel circuit is disposed between the two Y capacitors, the primary winding of the second transformer has a terminal connection, the transformer has a second secondary winding, the secondary winding and the second secondary winding of the transformer each have a terminal connection, the direct voltage terminal connection of the bridge rectifier, the terminal connection of the controllable switch, and the terminal connection of the secondary winding of the second transformer are at ground at a primary side, and the third common connection point, the terminal connection of the primary winding of the second transformer, and the terminal connection of each of the secondary winding and the second secondary winding of the transformer are at ground at a secondary side.
In accordance with still a further feature of the invention, the secondary winding of the transformer has a winding direction to form a forward converter.
In accordance with still an added feature of the invention, the secondary winding of the transformer has a given winding direction and the second secondary winding of the transformer has a winding direction opposite to the given winding direction to form a flyback converter.
In accordance with still an additional feature of the invention, there is provided a fourth capacitor and a fourth diode are connected in parallel to form a third parallel circuit with first and second terminal connections, the third parallel circuit is disposed between the two Y capacitors, the first terminal connection of the third parallel circuit being at ground at a secondary side and the second terminal connection of the third parallel circuit being connected, through the second diode, with the second common connection point, second and third resistors connected together to form a first voltage divider, the first voltage divider divided connected in parallel with the second capacitor and having a center tap, a common connection point of the secondary winding of the transformer and the second capacitor is at secondary-side ground, a common connection point of the second secondary winding of the transformer and the third capacitor is at secondary-side ground, the input of the pulse generator has a first supply voltage input and a second supply voltage input, the second supply voltage input is at ground at a secondary side, a second transistor has an emitter, a collector, and a base, a fifth series circuit includes an emitter-collector circuit of the second transistor, a fifth diode, and a sixth diode, the second common connection point is connected with the first supply voltage input of the pulse generator through the fifth series circuit, a third transistor has a collector-emitter path, and a base, a fourth resistor is connected to the collector-emitter path of the third transistor to form a sixth series circuit, the base of the second transistor is at secondary-side ground through the sixth series circuit, the base of the third transistor is connected to the center tap of the first voltage divider and to the collector of the second transistor through a fifth resistor, a fourth transistor has an emitter and an emitter-base path, a fifth transistor has a base and a collector-emitter path, the emitter-base path of the fourth transistor, a sixth resistor, and the collector-emitter path of the fifth transistor are connected to form a seventh series circuit, the first supply voltage input of the pulse generator, to which the sixth diode is connected, is at secondary-side ground through the seventh series circuit, seventh and eighth resistors are connected to form a second voltage divider having a center tap, the second voltage divider is connected in parallel with the third capacitor, the center tap of the second voltage divided is connected with the base of the fifth transistor, the supply voltage input of the control unit has first and second supply voltage inputs, the second supply voltage input is at ground at a secondary side, the emitter of the fourth transistor is connected to the first supply voltage input of the control unit, a second transformer has a primary winding and a secondary winding with a first terminal and a second terminal, an RC element has a fifth capacitor and a first resistor, the RC element is connected to the primary winding of the second transformer to form an eighth series circuit, the output of the pulse generator is connected to ground at a secondary side through the eighth series circuit, the first terminal the secondary winding of the second transformer is at ground at a primary side, the controllable switch is a transistor with a gate electrode, and the second terminal of the secondary winding of the second transformer is connected with the gate electrode of the controllable switch.
In accordance with another feature of the invention, the fourth transistor has a collector, an infrared amplifier has first and second supply voltage inputs and an output, the collector of the fourth transistor is connected with the first supply voltage input of the infrared amplifier, the second supply voltage input of the infrared amplifier is at ground at a secondary side, and the output of the infrared amplifier is connected with the supply voltage input of the control unit.
In accordance with a further feature of the invention, there is provided a voltage stabilizer disposed between the collector of the fourth transistor and the control unit and the infrared amplifier.
In accordance with an added feature of the invention, the control unit is a microprocessor.
In accordance with an additional feature of the invention, the starting circuit including the second through sixth diodes, the second through eighth resistors, and the third, fourth, and fifth transistors is an integrated circuit.
In accordance with yet another feature of the invention, the input of the pulse generator is a supply voltage input and the first input is connected to the second common connection point.
In accordance with yet a further feature of the invention, the pulse generator has a second voltage detection input and the second voltage detection input is connected to the second common connection point.
In accordance with yet an added feature of the invention, dependent upon a signal at the second voltage detection input, the pulse generator is adapted to assume one of a first state in which no drive pulses are available at the output of the pulse generator and a second state in which drive pulses are available at the output of the pulse generator.
In accordance with a concomitant feature of the invention, the at least one direct voltage output is a plurality of direct voltage outputs.
The inventive starting up of the switch-mode power supply takes place in four steps.
In the first step, energy is collected at the alternating voltage input of the bridge rectifier, and is transferred to a capacitor of the secondary side of the switched-mode power supply. In the following second step, the pulse generator is switched on when the energy transferred to the capacitor (or, in other words, the voltage at the capacitor) reaches a predeterminable first minimum value. In the subsequent third step, due to the switched-on pulse generator the output voltage of the switched-mode power supply slowly builds up to the target value. Finally, in the fourth step, which terminates the starting up, the control unit controlling the pulse generator is switched on when the output voltage of the switched-mode power supply reaches a predeterminable second minimum value. Thus, the pulse generator and the control unit that controls it are switched on one after the other during the starting up of the switched-mode power supply.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for starting up a switched-mode power supply, and switched-mode power supply having a starting circuit, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.